In a digital computer system which includes data written into memory as part of a read-modify-write operation, the data typically includes an error correction code (ECC) which extends over a number of consecutive bytes of data. When read data from the memory is to be modified by new data and then written into a selected address of the memory and the read data to be modified has a length less than the number of bytes necessary to generate the associated check bits for the error correction code (ECC), it is then necessary to read the entire selected address before merging the new data with the read data in order to properly generate new ECC check bits for the modified data which is rewritten. For instance, in the typical read-modify-write memory cycle, if four consecutive bytes of read data are necessary to generate corresponding check bits for the error correction code (ECC), and if only one byte of data of four consecutive bytes of read data is to be modified, then it is nevertheless necessary to read the entire four bytes of data in order to generate check bits for the modified data.
The procedure generally used for read-modify-write operations as described above has involved a read buffer for storing the entire contents of the memory address selected for modification with new data and a write buffer for storing the modified data for the selected memory address until the modified data could be rewritten. In addition, when two write commands were required, there would be a separate input data buffer for each command. The large amount of buffer storage required in the generally used read-modify-write data path is undesirable.